"This is my last election,” Obama said. “After my election, I have more flexibility."

"I will transmit this information to Vladimir," said Medvedev, who will hand the Russian presidency over to Vladimir Putin in May.

The White House confirmed that the private conversation took place in the context of a public conversation regarding NATO’s plans for missile defense in Europe and the need for bilateral cooperation between the United States and Russia. Russia has expressed concern that the United States has not offered satisfactory guarantees that a European missile defense system would not be aimed against Russia, and the subject has increased tension between the two countries.

"Since 2012 is an election year in both countries, with an election and leadership transition in Russia and an election in the United States, it is clearly not a year in which we are going to achieve a breakthrough," deputy national security adviser Ben Rhodes said in a statement.

"Therefore, President Obama and President Medvedev agreed that it was best to instruct our technical experts to do the work of better understanding our respective positions, providing space for continued discussions on missile-defense cooperation going forward."

Rhodes further clarified at a press briefing on Monday that while the two leaders acknowledged differences on the issue of missile defense, “they did agree that we should continue to be working on this issue at the technical level; that there are steps that can be taken on both sides to gain better understanding of the U.S. and Russian positions.”

Obama has suffered political fallout in the past from similar incidents. Last April, the president was caught on a live microphone during a private conversation at a fundraiser, apparently complaining about Republicans. Last November, reporters accidentally heard a conversation between Obama and French President Nicolas Sarkozy where the two leaders commiserated over dealing with Israeli Prime Minister Benjamin Netanyahu.

Both comments, likely intended to remain private, were picked up by opponents and used to criticize Obama.

Reaction to the Medvedev conversation came swiftly on Capitol Hill. Rep. Mike Turner (R-Ohio) shot off a letter to the president demanding an “urgent explanation."

Turner, chairman of the House Armed Services subcommittee that deals with nuclear issues, accused Obama of walking away from his promise that “Russian concerns about missile defense will not be allowed to affect U.S. missile defense deployment plans.

“Congress has made exquisitely clear to your administration and to other nations that it will block all attempts to weaken U.S. missile defenses,” wrote Turner, who has been a frequent critic of the administration’s nuclear policies and implementation of the New START treaty with Russia.

“I want to make perfectly clear that my colleagues and I will not allow any attempts to trade missile defense of the United States to Russia or any other country,” he said.